IIAC Reviews Risk of HAVS from Motorcycle Handlebars

In April of this year, the Industrial Injuries Advice Council (IIAC) published an Information Note, after having considered the possibility of extending the prescribed disease of Hand Arm Vibration Syndrome (HAVS), under the Industrial Injuries Disablement Benefit (IIDB) Scheme.[i] Each prescribed disease has corresponding prescribed exposures/causes. In order to make additions to this list, the IIAC generally seeks evidence that exposure will ‘double the risk’ of developing HAVS.

In January 2017, a claimant purported to have developed Raynaud’s phenomenon, a type of HAVS, as a result of riding a motorcycle during his employment. It was inferred that vibrations, emanating from the handlebars were the cause, but ‘motorcycle handlebars’ have not yet made the ‘qualifying list’ of tools and equipment, specified for HAVS, which currently includes ‘chain saws, riveting hammers, swagers and road breakers’.

HAVS is an umbrella term for upper-limb disorders associated with substantial hand transmitted vibration, which can be expressed as Vibration Induced White Finger (VWF) and digital neuropathy, a sub-type of Raynaud’s phenomenon. The most common symptom of Raynaud’s is the marbling of the hands’ extremities (furthest from the heart), due to a ‘temporary interruption of blood flow’. When normal blood circulation restores, affected body parts often tingle and turn from blanched to ‘fiery red’.

VWF is a common occupational disorder, but should be distinguished from Primary Raynaud’s, which occurs naturally in 5-10% of men and 10-20% of women, and Secondary Raynaud’s, which is attributable to rheumatic diseases, blood disorders, drugs, or traumatic injury.

All of the vibratory equipment listed as a prescribed cause of HAVS by the IIAC produce high vibration magnitudes that satisfy the requirement of ‘doubling the risk’ of HAVS. This is evidenced by surveys of long-term user groups.

Firstly, the IIAC questioned whether, in order to add motorcycle handlebars to the list, the levels of exposure could be defined by their dosage of hand transmitted vibration, rather than by groups of equipment, on the basis that ‘modern control standards assume a specific relationship between dose and risk of VWF’.

However, the Information Note detailed several issues with a ‘dosage’ definition:

  1. The relationship between dose and effect is disputed between scientists in the field.
  2. The best metric for assessing dosage of exposure is a subject of dispute.
  3. There is a wide variation (up to 5-fold) in exposure levels recorded between different brands of the same tool; identical tools in different stages of maintenance; tools used in different ways; and tools ‘worked’ against different surfaces and materials.
  4. Errors are often made in reconstructing exposure durations and patterns.
  5. Interpreting the causes of Raynaud’s is a challenge.
  6. Claims are assessed in a high-volume environment without recourse to detailed proofs which could address inherent dose assessment uncertainties, claim by claim.

To date, there have not been many studies on the health effects and exposures arising from handlebar vibration. In the largest of the Japanese surveys, 2.1% of 100,000 mailmen using motorcycles were found to have VWF symptoms.[ii] Moreover, ‘white finger symptoms were about twice as common, and finger numbness about 1.4 times as common in those with >15 years of motorcycle exposure at >200 km/week than in those with >15 years of motorcycle exposure at <200 km/week (and increased but not doubled in those with 10-14 years of driving)’. Unfortunately, ‘no analysis has resolved the impact of age versus exposure duration on symptom prevalence’, so understanding the relevance of higher VWF rates recorded by those who were more experience drivers or those who happened to drive further on a daily basis, became a challenge. This conundrum was only exaggerated by the fact that the group who drove further distances were exposed to cold conditions, which is a trigger for Raynaud’s attacks and could have negatively influenced a genuine VWF finding.

On this subject, the author of the report, Tominaga, admitted that:

“an operation combining severe cold exposure with weak intensity vibration exposure”, was inclined to ascribe the reported symptoms largely to primary Raynaud's phenomenon rather than VWF’.

At the Institute of Sound and Vibration Research, they compared the vibration levels created by 750cc motorcycles used by the police with four-stroke single-cylinder engines used by postal delivery men; the police were deemed to be exposed to much higher vibration levels using the 750cc motorcycles.

Concurrent with the issues relating to ‘dosage’, the institution noted that ‘variation by road surface (worse on unmade roads and in forests) and by era (such that when anti-vibration measures were introduced in Japan around 1980 they reduced exposure magnitudes by about two-thirds)’. The fact that the motorcycle industry has prioritised ‘brand image’ and ‘performance’, rather than ‘vibration control’ has only increased the range of vibration levels which handlebars emit.

Nevertheless, a vibration specialist at the Institute, suggested that:

‘... the scientific literature is rather patchy, but shows that the vibration on the handlebars of bikes can be of sufficient magnitude to anticipate a risk meriting control measures … the potential for vibration on the handlebars of motorbikes to cause the condition is sufficiently well recognised for it to be a matter that is commonly considered as an alternative explanation for symptoms in civil claims for compensation’.

On the other hand, in a British National Survey of Vibration:

‘... the median vibration magnitude assigned motorcycle handlebars (of 1.5 m/s2 ahw) was well below assumed median values for vibratory tools prescribed already under the IIDB Scheme (e.g. 12m/s2 for rock drills, 29 m/s2 for scabblers, 10 m/s2 for chain saws, 16 m/s2 for needle guns (Palmer et al, 2000a))’.

Ultimately, the IIAC reached the conclusion that proving whether the risk of finger blanching ‘more than doubles’ when riding motorcycles cannot be ‘robustly’ and ‘practically’ defined by the scheme. Consequently, the IIAC decided against adding motorcycle handlebars to the list of prescribed causes of HAVS, but will continue to monitor future research, if and until the moment when prescription of VWF is sufficiently developed.

 

 

[i] ‘Prescribing for Hand arm Vibration Syndrome and risk from motorcycle handlebars: Information Note’ (April 2017 Industrial Injuries Advisory Council) <https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/613918/hand-arm-vibration-syndrome-and-risk-from-motorcycle-handlebars-iiac-information-note.pdf> accessed 15 June 2017.

[ii] Tominaga Y, ‘Low intensity vibration in postmen and their disorders. Proceedings of the Japan Informal Group on Human Response to Vibration, held at National Institute of Industrial Health, Kawasaki’, 1-3 July 1994a, 64-66 <http://citeweb.info/19950554133> accessed 15 June 2017.